M271 rattling only when hot

[AlexandarAtan]

I have a 2012 C180 CGI with an M271 EVO engine and I’m facing an issue.

Coolant started mixing with oil. I went to my mechanic, who determined that the problem was with the oil filter housing and the oil cooler. After replacing them, the coolant kept getting contaminated with oil (he just hadn’t flushed it properly). Then, he decided that the head gasket needed to be replaced and the cylinder head checked for cracks.

In the end, the gasket wasn’t torn, and the head wasn’t cracked. After many flushes, he finally managed to get clean coolant, but after all this, a new problem appeared.

Once the engine reaches operating temperature (especially after longer drives), a metallic rattling/knocking noise starts coming from the front of the engine. The noise sounds like metal parts hitting each other and is heard only at idle or when the car is in gear but stationary. When the engine is cold, there are no issues, and it sounds perfect. I noticed that after an oil change (5W-40, 229.5), the noise is significantly reduced for the first 300-400 km, but it doesn’t disappear completely. If I rev the engine to around 5000 RPM and then let off, the rattling stops for about 30-40 seconds.

Video of the noise: Video

Thanks in advance!

Best regards!

 

[Tonygw]

Have you checked the timing chain for slack? Known issue on these and can manifest itself in many ways, chain is at the front.

 

[markjay]

Have you checked the timing chain for slack? Known issue on these and can manifest itself in many ways, chain is at the front.

As above.

With this particular engine (M271), it would be a shame not to renew the timing chain, hydraulic tensioner, and guide, when the head came off. The camshaft sprocket wheels only need replacing on condition.

 

[AlexandarAtan]

This is how the chain and guides look with the valve cover off.

Chain
Guides